#include <iostream>
using namespace std;
int count(int id){
	if(id==1){
		return 1;
	}
	else if(id==2){
		return 2;
	}
	else{
		return count(id-2)*2 + 1 + count(id-1);
	}
}

int main(){
	int id = 7;
	cout<<count(id)<<endl;
}
